In a sensational feat for science and international collaboration, a team of more than 200 researchers using a "virtual telescope" of observatories around the world for the first time managed to see and photograph what was previously unseeable: a supermassive black hole.
The Event Horizon Telescope — an international organization linking eight major radio observatories on four continents into one virtual, Earth-sized telescope with previously unavailable resolution and sensitivity— pulled off one of astrophysicists' longtime dreams.
By exploiting the Earth's rotation, the array functioned as one virtual "Earth-size telescope" with enough of an angular resolution to read a newspaper in New York from a sidewalk café in Paris, according to EHT.
It directly observed the immediate environment of a supermassive black hole with angular resolution comparable to the event horizon — the boundary of a black hole beyond which nothing, no light or matter, can escape from within it.
The first photo ever made of a black hole showed a fiery ring of orange and black, with light swarming around the edges of it. The supermassive black hole depicted is as big as our solar system.
“We have seen what we thought was unseeable. We have seen and taken a picture of a black hole,” said EHT's Director Sheperd Doeleman, a senior research fellow at the Harvard-Smithsonian Center for Astrophysics, who led the scientific team spanning 20 countries.
"We have achieved something presumed to be impossible just a generation ago," he said. "Breakthroughs in technology, connections between the world's best radio observatories, and innovative algorithms all came together to open an entirely new window on black holes and the event horizon."
To make it all work, EHT first had to upgrade and connect a worldwide network of eight preexisting telescopes at challenging high altitude sites in Antarctica, Chile's Atacama Desert, mountains in Arizona and Spanish Sierra Nevada and volcanoes in Hawaii and Mexico.
The radio telescope array offered scientists a new way of studying the most extreme objects in the universe predicted by Albert Einstein’s general theory of relativity. The image itself helped to confirm his theory; Einstein even predicted the black hole's symmetrical shape.
55 million light years away
The EHT called it the first direct visual evidence of a supermassive black hole and its shadow while announcing the breakthrough in papers published in a special issue of The Astrophysical Journal Letters.
The image revealed the supermassive black hole at the center of Messier 87, a massive galaxy in the Virgo galaxy cluster. The black hole is 55 million light years from Earth — a light year equals 9.5 trillion kilometers— and has a mass that is 6.5 billion times that of the Sun.
Supermassive black holes, located at the center of most galaxies, are distinct from smaller black holes formed by collapsed stars. But the measurements occurred at a wavelength invisible to the human eye, so scientists added gold and orange to the image of the black hole to depict the heated light and gas circling around it.
The image was based on telescope data collected over four days more than two years ago. Hundreds of researchers and scientists put it together using supercomputers. MIT graduate student and computer scientist Katie Bouman developed an algorithm to crunch the five petabytes of data from eight radio telescopes.
Black holes are extraordinary cosmic objects, EHT said, with enormous masses but extremely compact sizes.
"If immersed in a bright region, like a disc of glowing gas, we expect a black hole to create a dark region similar to a shadow — something predicted by Einstein’s general relativity that we’ve never seen before," said Heino Falcke, chair of EHT's science council and professor of radio astronomy and astroparticle physics at Radboud University in the Netherlands.
"This shadow," he said, "caused by the gravitational bending and capture of light by the event horizon, reveals a lot about the nature of these fascinating objects and allowed us to measure the enormous mass of M87’s black hole."
